Stratification techniques
- Definition of the stratification technique
Direct layering restoration is a technique that consists of superimposing layers of composite resin with different optical characteristics so that the result is as close as possible to the natural dental organ. The result obtained varies depending on the technique and the material used.
- Principles
- The tooth is made up of three hard tissues (enamel, dentin and cementum) which, due to their locations and compositions, determine the color of the natural tooth.
- The optical specificities of these tissues vary significantly. Therefore, it is impossible to restore the original optical characteristics of the tooth with a single restorative material if the cavity consists of both dentin and enamel.
- This is how most composites are now composed of two main types of base masses, enamel masses and dentin masses, whose optical properties are similar to the different dental tissues.
- The principle is to restore the basic shade of the tooth by superimposing different masses of composites of different shades and translucency.
- Indication of stratification
- Amelogenesis imperfecta
- Agenesis of maxillary lateral incisors
- Closure of unsightly interdental spaces or multiple diastemas
- Site 2 restorations caused by proximal carious lesions
- Replacement of old composites
- Coronary fractures
- Absolute contraindications
• Inability to obtain a watertight operating field.
• Preparation limit beyond the enamel-cementum junction.
• Too much loss of substance (dilapidated tooth)
• Patient at high risk of caries and/or insufficient oral hygiene.
• Allergies to one or more components of the composites used in lamination
Relative contraindications
• Shade, shape and hermeticity of large and numerous restorations
• Very characteristic teeth (elderly people).
Stratification techniques
- The different stratification techniques
5.1 Historical two-layer technique
This concept was based on a monolaminar chromatic construction of the restoration, plus a translucent incisal shade on the surface to mimic translucency and possibly also opalescence
Most of these composite systems consisted of a set of masses, usually according to the Vita Classic shade guide system, offering different shades (A to D) in different chroma levels (1 to 4, depending on the shade group).
Body tones exhibited intermediate opacity (between natural dentin and enamel values)
Even though this is a layering approach, the aesthetic quality of the restoration remains generally limited.
5.2 The classic trilaminar approach of 1991
This technique is based on a polychromatic reconstruction using opaque dentin masses, body enamel masses, and transparent incisal.
These are the chromatic dentin and enamel shades, which follow the VITA shade guide system (different shades: A to D, different colour: 1 to 4, depending on the shade group), supplemented by one or more translucent incisal shades.
The different masses do not correspond to the real optical properties of natural tissues, so it is impossible to perfectly follow the Natural model
Dentin masses have an opacity close to or greater than that of natural dentin, while enamel has an opacity intermediate between natural dentin and enamel.
The aesthetic results are better but difficult to obtain due to the subjectivity of the distribution of the different masses of composites.
5.3 The modified Trilaminar technique of 1996
This concept is actually based on the application of two basic masses which more faithfully reproduce the optical properties of natural tissues and then allow a spatial arrangement closer to the natural structure of the tooth.
Dentine Opaque/Body Shades are available in different shades (Vita Shades A to D) with varying chroma and two levels of opacity
The enamel shades were developed according to the concept of “natural layering” which involves the use of three different basic translucent enamel shades (white, neutral and ivory grey) and some additional shade/translucency variations to expand the system options: clear enamel (CE), white enamel (WE), yellow enamel (YE), amber enamel (AE), grey (GE) and very bright (XL); a characteristic brand is Esthet-x (Dentsply)
This approach certainly represents an improvement over the basic trilaminar approach, although good clinical judgment is required in choosing the appropriate number of layers.
5.4 The 2000 Natural Layring Shading Bilaminar Approach
- The use of a natural tooth as a model proposed by Dietshi allowed a logical evolution of direct restorative materials, leading to an improved concept of layering that is named after the source of inspiration which is nature.
- It is in fact the result of an in-depth study of the natural optical properties of dentine and enamel, taking into consideration all the modifications that a tooth can undergo due to age or function.
- Spectrophotometric measurements of natural teeth allowed us to conclude to use two composites, one for dentin and one for enamel. They are placed in layers of the same thickness as the tissues they replace, with the only difference that the dentin covers part of the enamel bevel to hide the transition between the restoration and the tooth.
Stratification techniques
The Vita shade guide is most often abandoned in favor of a specific shade guide
- In an NLS composite system, the specific optical properties of dentin are a unique shade, unique opacity and a wide chromatic range.
- For enamel, three specific types of enamel are needed. To imitate young enamel: white shade and reduced translucency; adult enamel: neutral shade and intermediate translucency; and for aged enamel: yellow shade and higher translucency, (typical brands: Miris and Miris2 [Coltenewhaledent], Ceram -Xduo [Dentsply], Enamel HFO Plus [Micerium], and inspiro, EdelweissDR).
5.4 The advanced technique of “Natural Layering shading”
- This more ambitious technique is an evolution of the Natural Layering Concept technique.
- For teeth with a richer colour composition special effect shades produced in a fluid consistency are available in some NLS systems to achieve the patient’s aesthetic desire.
- These materials are most often added between the layers of dentin and enamel.
- The Polychromatic Approach
- This lamination technique offers the use of several working modes that do not depend on a protocol dictated by a specific commercial brand of composite.
- The concept, called polychromatic stratification (Fahl, et al) is defined by the variation in dentin and enamel shades.
- Dentin shades can be either VITA-based or non-VITA-based.
- Enamel shades are subclassified into:
• body enamel
• valuable enamel
• translucent effect enamel
• semi-translucent, milky white enamel.
The actual number of layers in a given restoration will then be determined by the polychromatism of the tooth. For example, in fairly monochromatic teeth with little or no incisal translucency, two or three shades may be sufficient. For more polychromatic teeth, with accentuated incisal characterizations, five or even more shades may be indicated.
5.6 Three-layer technique according to Vanini using HFO or HRI enamel:
- It is a technique close to the three-layer technique which was proposed in 1996.
- The main difference between these two techniques lies in an additional layer of adhesive resin used between the dentin and the enamel. Its purpose is to mimic the amorphous and high protein enamel layer called by Vanini the high diffusion layer or vitreous layer. This technique allows for optimal aesthetic integration of anterior composite restorations, faithfully reproducing the variations in shade and translucency of natural teeth.
HFO and HRI refer to types of aesthetic composites used in restorative dentistry, particularly in the Vanini three-layer layering technique .
- HFO (High Filler Opacity) This is a highly filled composite, offering good opacity and excellent mechanical strength. It is often used to imitate dentin due to its optical and mechanical properties.
- HRI (High Refractive Index) It is a high refractive index composite , designed to improve light transmission and optical integration with the natural tooth structure. It is used for the enamel layer , allowing to obtain a translucency close to that of natural enamel.
Stratification techniques
Application in the three-layer lamination technique according to Vanini:
- 1st layer (Dentine): Opacified composite (eg HFO) to reproduce the saturation of the color.
- 2nd layer (Effects): Possible addition of internal effects (e.g. modified tints, opalescences).
- 3rd layer (Enamel): Translucent composite (eg HRI) to restore the translucency and shine of natural enamel.
- In large restorations Vanini describes the use of three different dentins applied in oblique layers . It is important to note that the oblique contributions, in addition to favoring the aesthetics, improve the contraction forces within the composite. If the restoration is of smaller volume, the number of different dentins decreases.
- Unlike the classic three-layer techniques, the shade is not defined by the Vita shade guide but in a particular shade guide where the dentines are called UD1 to UD6.
- Opaque dentin is replaced by dentin that is two shades brighter than the body dentin. For example, for an A3 restoration (UD3), the most palatal dentin will be UD5 dentin. In this case, if the restoration is large in volume, there will be UD5, UD4 dentin, and UD3 dentin: UD5 and UD3 if the restoration is smaller in volume, and if the volume is small, only UD3 dentin.
- If a composite of the HRI system is to be used, a layer equivalent to that of the replaced tissue (enamel) is put in place because the refraction coefficient of the HRI composite is equivalent to that of the enamel.
- If the enamel is that of the HFO system, it must be placed in a thinner layer than the one it replaces.
- The different stages of stratification
- Choice of shade (Define the tooth’s chromatographic map)
Tooth shade is the result of an equation that involves several factors, so its careful analysis is essential to highlight the unique characteristics of each tooth.
Shade taking is often done with a Vita shade guide on a clean mouth, before preparation, placement of the dam and on hydrated teeth.
– Lighting: turn off the surgical light and any stray lighting (neon lights).
-Place the patient in front of a dimly lit window with natural light
-Remove interfering colors (red scarf, red lipstick, bright makeup)
-Work with the naked eye for colors and with a magnifying glass for surface condition details
To get an idea of the final shade of the tooth, it is necessary to position and polymerize small masses of the composite chosen previously at the level of:
-from the junction of the middle third and the cervical third of the tooth (most saturated area of the tooth) for the shade of the dentin.
-from the free edge (most translucent area of the tooth) for the enamel shade.
Once the shade has been validated, the composite pads can be easily removed with a spatula.
Noticed
- Depending on the age, a tooth can be characterized. More translucency for a young tooth and more saturation for an old tooth.
- The color of the periodontium influences the choice of shade
- Be careful with the color of the canines, which are more saturated.
- Try to match the shades with the neighboring teeth as much as possible.
- If the tooth is too dilapidated, the shade must be taken from the adjacent tooth.
- Step by step method of stratification
Stratification is carried out in several stages
Establish the tooth’s color map
This is a fundamental step and must be carried out meticulously, with attention to detail in mind. The observation is structured around three areas.
- Cervical region with thin enamel.
- Middle region We will determine the degree of saturation.
- Incisal third: This is the area of greatest animation where we really bring our restoration to life.
It is important to observe the internal dentin architecture and map it on a diagram, to note the areas of translucency, the presence of opalescence effects, the chromatically saturated areas (hypoplasias) and their location, the anatomy of the free edge.
This careful observation highlights the structural organization of this type of restoration and leaves no room for subjectivity.
Stratification techniques
- The VANINI Chromatic Map
Tooth color is the complex result of several factors that must be carefully analyzed.
According to VANINI, tooth color is composed of 5 dimensions.
These dimensions are based on four main hues, depending on age: yellow-orange, white, blue and orange.
5 dimensions of Vanini exist:
- Chromaticity:
Chromaticity corresponds to the hue and saturation of the internal dentin mass.
- Brightness:
Brightness is determined by the quantity and quality of the enamel : its thickness, degree of mineralization and water content.
- Intensive:
Intensities are features located on the surface of the enamel of a natural tooth. They represent areas of lesser enamel mineralization.
- Opalescence:
Opalescence is a phenomenon visible throughout the enamel but is important at the incisal edge because the light then only passes through the enamel without interference with the dentine.
Type 1: nipple, Type 2: split central nipple, Type 3: comb-shaped. Type 4: window. Type 5: spot.
Characterizations:
- They are classified into five types: nipple, banded, margin, spot and crack.
- They come in white, amber and brown.
- Edge characterization allows the white border often present at the end of the incisal edge to be recreated.
Noticed
By completing the color chart the practitioner will have a theoretical guide and a road map that must be followed during each stage of the restoration by stratification.
Stratification techniques
- Making the silicone key
This step can be done in two ways:
-either at the Wax-up prosthesis laboratory: after taking an impression, the laboratory makes us a plaster model with a wax-up on the tooth to be reconstructed. The silicone key will therefore be taken from the model.
-either in the same session, in the chair by Mock-up: the tooth is first reconstituted in non-glued composite. This reconstruction must meet the anatomical-functional criteria of the tooth (aesthetics, functionality and phonetics). The silicone guide (or key) can then be made.
Noticed
If it is a question of remaking an already existing composite that has an aesthetically and functionally suitable shape, a simple recording of the situation using a silicone key may be sufficient.
- Cavity preparation
- For an optimal aesthetic result, the teeth must be prepared in such a way that the boundary between the composite and the tooth is not visible, which gives an unsightly effect.
- A peripheral bevel should be made around the entire periphery of the enamel preparation . It should be short (1 mm), oval, angled and thick (1 to 3 mm in the enamel).
- Its implementation is essential because it allows:
-reduction of micro-infiltrations at the tooth/composite joint,
-improved adhesion thanks to the increase in the etched surface,
-good aesthetics by allowing enamel coverage with a greater quantity of material,
-better diffusion of light between the tooth and the restoration.
This bevel will be polished to increase wettability and reduce voids at the
6.5 Setting up the operating field
- The surgical field can be placed before or after tooth preparation.
- The establishment of a surgical field (or dam) is essential for hermeticity in any bonding procedure. It will concern at least the four incisors and the canines in order to be able to better control the clinical stages.
- Additionally, the dam will allow slight gingival retraction, facilitating access to the preparation limits.
Stratification techniques
6.6. Stratification
- Etching and bonding
- Placement of the silicone guide and creation of the palatal wall.
- Placement of the proximal wall
- Placement of dentin masses
- Realization of the high diffusion layer
The high diffusion layer is achieved by placing a white, high fluorescence resin applied to the palatal enamel and the dentin mass. The glass connector aims to mimic the amorphous enamel layer with high protein content.
- Implementation of Intensive and Opalescent characterizations
- Creation of the enamel wall
6.7 Control of occlusion, phonation and aesthetics
6.8 Finishing and polishing
- First, the general anatomy of the tooth is retouched by the use of discs with increasingly finer grains.
- Transition lines, concavities and micro texture are highlighted using a pencil or articulating paper applied to the vestibular surface of the adjacent tooth
- Then, we will use a silicone cup which, thanks to its low abrasiveness, allows us to polish the surface without erasing what we have just drawn.
- In a third step, we will focus on the micromorphology of the restoration; with a silicone cup, high-grain diamond bur, brush and diamond pastes, the micro-texture is achieved by delicate lateral movement to obtain a non-uniform dental surface.
- Finally, comes the polishing and buffing phase. Polishing is carried out using a brush and diamond pastes, with decreasing grain size (from 3 to 1 micron), which, when passed at low speed, make the surface shiny without altering the macro or micromorphology carried out previously.
- Reconstructions by stratification on posterior teeth:
Layering techniques improve the quality of restorations because they allow for more careful control of polymerization shrinkage. As the surface area of the restoration bonded to the tooth increases, or as the number of edges of the restoration increases, the stresses associated with polymerization shrinkage will increase.
7.1 The horizontal stratification technique
It can be considered for small cavities. This technique involves placing layers horizontally, one on top of the other, and their individual polymerization. The occlusal relief is shaped with the last layer. This technique is very simple but can complicate the sculpture of the occlusal surface.
7.2 The oblique stratification technique
Occlusal anatomy is easily reproduced using the oblique layering technique. However, this technique can cause problems regarding the homogeneous adaptation of the different layers. The risk of heterogeneity (inclusion of air bubbles) increases because the individual layers converge at rather acute angles, particularly at the bottom of the cavity.
7.3 The centripetal stratification technique
A centripetal layering technique is recommended. This technique will transform a Class II into a Class I. It is important that the first layer, in contact with the matrix, be as thin as possible. For large cavities, two layers may be applied one after the other so that the first extends along the matrix from the cervical part to the middle of the cavity, while the second will continue to follow the matrix from the middle of the cavity to its apex.